Luckily his family were able to get in touch with him. His grandmother Gerry Constable said, “He’s doing okay, he’s safe because he’s in a flat off the ground.

“He sent us a video of the road outside where he is staying. It’s very dark, there’s the sound of pounding rain, the water flowing down the road. And that’s in a safe area.

“I can’t imagine the amount of rain falling out the sky, and seeing things filling up.”

She said Joshua had had a ‘whale of a time’ on an adventure volunteering with Camp America in Texas. With one free month left at the end of his stay to go travelling, he visited a friend in central Houston when disaster struck.

Mrs Constable said, “He thought he would only be there for a few days and he got stuck. They ran out of food – shops were emptied very quickly.

“He queued for two hours in the absolute pouring rain for supplies and said of the couple he is staying with, one of them works in a school and it’s completely underwater.

“His biggest problem is he can’t get on a flight to come home, so they transferred him to Houston airport, but he had left his passport back at the camp.

“He’s totally marooned now because there’s no buses, nothing. He’s in touch with the camp and is due to fly home next Wednesday [September 6] if he can get back to the site in Austin, which is about 200 miles away. It’s a waiting game now until they get the buses on the move.”

She said he is frustrated because he and his friend cannot do anything to help but simply have to wait it out.

“He can’t be of much use to anybody, he’s been sitting it out,” she said, “They are used to helping people and would have felt better if they could have done something useful.

“He took no wet weather gear or long trousers, he’s been working in 102 °F.

“The devastation is awful, we are seeing more than they are because TV is very limited.”

Thousands of people have left their homes seeking emergency shelter from the severe flooding which left large parts of Houston underwater after a record-breaking 51 inches of rainfall.